The background of the invention is the wireless payment of charges for the use of roads (road toll) by vehicles. Systems provided for this purpose have been delivered by the Q-Free ASA company since many years. Nowadays these systems are used in Norway and are well known under the term “Q-Free-box”. In this connection the term “box” is related to the module of this system attached to an individual vehicle, that is to say to a so-called transponder. This transponder receives data from a main station of the transponder system and as an answer on this transmitts individual data back to the roadside. Meanwhile the technological development in this field has turned to transponders which—contrary to transponders formerly used in this field—are being operated not passive, but active and for the operation of which microwave radiation with frequencies in the range of 5.8 GHz is applied. With this known transponder system the radiation received by the transponder is amplitude modulated for the transmission of data, while the microwave radiation transmitted by the transponder for the transmission of data is phase modulated.
The modulated input signal obtained in the transponder by the reception of the microwave radiation initially is demodulated for obtaining a binary input data sequence (of an input data frame). Then this input data sequence is fed to a digital processor (microcontroller) operated by a processing clock of preset clock frequency for decoding and further processing of the received data as well as for generating of a binary output data sequence (output data frame). During a certain duration from the output data sequence as an answer to the input signal an output signal is formed in the transponder which as modulated microwave radiation of certain frequency is irradiated over the antenna of the microcontroller.
These active transponders are as energy source provided with a battery. In this connection the term “battery” comprises electrical primary cells as well as electrical secondary cells in a single oder in a multiple arrangement.
With the known transponder systems the succeeding transactions (transaction sequencies) between the main station of the transponder system and the individual transponder are carried out on the basis of an advanced communications protocol (HDLC—High Level Data Link Control) and usually contain the processing of data sequencies and control fields. Furthermore there is a considerable need for the security of the transactions which are to be carried out. To the most common security algorithms belong DES (Data Encrypting Standard System) and Trippel-DES. However the application of these security algorithms usually means that with this the processing of data by the transponder becomes very time consuming.
To this day the most common solution for a transponder of the transponder system is a solution, with which a serial processor is applied as microcontroller. With this solution there is available flexibility for changes and it is possible to achieve satisfying transaction speed with the use of processors, which operate with a system clock rate with a clock frequency of 10 MHz and higher.
The greatest problem which consists with microcontrollers applied as communications controllers until now is that there from the relatively high clock frequency of the system clock results a relatively high load for the battery of the transponder, and this in view of the average height and the duration of the current (integral over the current pulses over the time withdrawn with the frequency of the system clock) as well as in view of the fact that the pulse-like occuring current withdrawal represents an exceptional load for the battery. Even if this current withdrawal does not mean so much for the life time of the components of the transponder so a current withdrawal of such an extent and id an especially pulse-like occuring way is problematical particularly at relatively low temperatures where the internal resistance of the battery is high.
Finally the microcontroller applied for the transponder until now is a serially operating processor. This means that such a processor is not ideal in view of the processing of data which can be processed parallel, especially not then when on the one hand processing-wise extensible actions (decoding) are necessary in the processor and on the other hand within a shortest possible duration after receipt of the input signal an output signal shall be emitted from the transponder.